Methylenedioxybenzene derivatives of the general formula ##STR1## in which R.sub.1, R.sub.2, R.sub.3 and R.sub.4, are hydrogen or alkyl group or a halogen atom or a group ##STR2## wherein R.sub.5 represents hydrogen or an alkyl group and R.sub.6 represents an alkyl group, are currently used as synergists for certain insecticides.
Wachs in U.S. Pat. No. 2,485,681 and U.S. Pat. No. 2,550,737 describes methylenedioxybenzene derivatives of the formula ##STR3## in which A is hydrogen or an aliphatic radical, R is an intermediate aliphatic radical, R.sub.1 is a hydrocarbon radical, m is 2 or more and n is 1 or more, in admixture with natural pyrethrins. One of the compounds under the scope of the Wachs patents is piperonyl butoxide, in which R is CH.sub.2, m is 2, n is 2, R.sub.1 is butyl and A is propyl. Such compound is widely used as a synergist for natural pyrethrins.
Barthel et al, in U.S. Pat. No. 3,070,607, describe compounds of the formula ##STR4## in which R is hydrogen, methyl, or ethyl; R.sub.1 is alkoxyalkyl or polyalkoxyalkyl; R.sub.2 is hydrogen, propyl, propenyl or allyl, to be used as synergists for natural and synthetic pyrethrins. Hedenburg, in U.S. Pat. No. 3,117,135, describes compounds of the formula ##STR5## wherein R is alkyl of from 1 to 4 carbon atoms, m is 2 or 3 and n is 1 or 2 and A is propyl or allyl, to be used as synergists for natural and synthetic pyrethrins.
British patent 1,159,089 describes compounds of the formula ##STR6## wherein R.sub.1 is hydrogen or an alkyl group, R.sub.2 is alkyl group and X is a halogen atom or the same ##STR7## group as above, to be used as synergist for pyrethrins.
Japanese patent application 58-110,504 (as reported in C.A. 99,171334) of Sumitomo describes compounds of the formula ##STR8## wherein R is CH.sub.3 or CH.sub.2 CH.sub.2 OC.sub.4 H.sub.9 to be used in controlling pyrethroid-resistant insects.
Japanese patent application 61-24586 of Sumitomo describes compounds of the formula ##STR9## wherein R is hydrogen or lower alkyl and n is 1, 2 or 3, to be used as synergists for pyrethroids, fenvalerate and carbamate type insecticides.
B. P. Moore and P. S. Hewlett, in J. Sci. Food Agric. Oct. 9, 1958, 666, describes the relatioshionship between chemical structure and synergistic activity with natural pyrethrins in methylenedioxybenzene compounds of graded complexity. There are described compounds of the formula ##STR10## wherein R is (CH.sub.2).sub.2 --O--(CH.sub.2).sub.6 --CH.sub.3 or (CH.sub.2 CH.sub.2 O).sub.3 --CH.sub.3. According to the publication, the synergism is specific to the methylenedioxy benzene group.
J. E. Casida et al., in Science 153, 1131 (1966), describing the metabolism of various methylenedioxybenzene compounds in relation to their synergistic action, state that such compounds synergize the insecticidal activity of almost all classes of insecticide chemicals. Piperonyl butoxide is reported.
Of all the above mentioned compounds, the most currently used as synergist for insecticides is piperonyl butoxide, which however is quite expensive, being prepared only from safrole, which in turn is obtained only from essential oils, notably of sassofrass. Safrol is listed as a carcinogen by the EPA.
Anyway, in all of the above patents and publications, there are used, as synergists, pure methylenedioxybenzene derivative compounds, which means that such compounds, whatever was their preparation, were isolated from the reaction mixture.